The present invention relates to a technique enabling a working machine attached to the rear of a tractor to move vertically by one switching operation of a vertically moving lever provided on a back-and-forth operating lever disposed at an operating portion of the tractor, and providing the back-and-forth operating lever with a sub-transmission operating device.
Conventionally, a tractor is equipped at the rear thereof with a working machine via a working machine attaching device. The working machine can be moved vertically by lift arms of the working machine attaching device rotated by extension and contraction of a hydraulic cylinder which is operated by rotative operation of a position lever or a vertically moving switch disposed at a side of a seat so as to switch a control valve.
When reversing at an end of a line in a farm, the tractor, provided with the position lever or the vertically moving switch at a side of a seat thereof for moving the working machine vertically, must be stopped or decelerated. The working machine is lifted by operation of the position lever or the vertically moving switch, and then the tractor takes a U-turn slowly or travels backwardly by operation of a transmission, so that the tractor with the working machine works along the next line. Thus, the transmitting operation and the vertically moving operation of the working machine are done separately for the reversal, so as to take a long time. Furthermore, since a large tractor with a heavy working machine is constructed such that the working machine moves down by dead load, the working machine cuts into the field deeply at the initial time of working, so as to make the depth of cultivating unstable.
Also, a conventional technique of changing the traveling speed of a tractor equipped with a hydrostatic transmission (hereinafter "HST") by operation of a back-and-forth operating lever is known. Such a traveling vehicle is conventionally provided with a sub-transmission in addition to a main-transmission, thereby enabling the traveling speed thereof to be changed at a plurality of steps. A sub-transmission lever for operating the sub-transmission is provided apart from the back-and-forth operating lever for operating the main-transmission.
Thus, in such construction comprising the main-transmission of the HST and the sub-transmission of gearing, the back-and-forth operation lever and the sub-speed changing lever are separately provided. The sub-transmission of gearing occasionally requires declutching. If a handle is operated for steering and simultaneously main-and-sub-transmission levers are operated for the particular transmission at work, the speed of the vehicle cannot be changed smoothly. Also, when a step of traveling speed is shifted from a low speed position to a high speed position and is returned to the original low speed position, the original low speed can hardly be obtained, thereby requiring the further transmitting operation, which in turn prevents the field from being cultivated equally.